Ignition timing in an internal combustion engine is the process of setting the time that a spark will occur in the combustion chamber (during the power stroke) relative to piston position and crankshaft angular velocity. Setting the correct ignition timing is crucial in the performance of an engine. The ignition timing affects many variables including engine longevity, fuel economy, and engine power. Modern engines that are controlled by an engine control units use a computer to control the timing throughout the engine's RPM range. Older engines that use mechanical spark distributors rely on inertia (by using rotating weights and springs) and manifold vacuum in order to set the ignition timing throughout the engine's RPM range. There are many factors that influence ignition timing. These include which type of ignition system is used, engine speed and load, which components are used in the ignition system, and the settings of the ignition system components. Usually, any major engine changes or upgrades will require a change to the ignition timing settings of the engine. A colorized automobile engine The internal combustion engine is a heat engine in which the burning of a fuel occurs in a confined space called a combustion chamber. ... A power stroke is, in general, the stroke of a cyclic motor which generates force. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... An Engine Control Unit (ECU) also know as Engine Management System (EMS) is an electronic system which controls various aspects of an internal combustion engines operation. ... This article is about distributors in internal combustion engines. ... The principle of inertia is one of the fundamental laws of classical physics which are used to describe the motion of matter and how it is affected by applied forces. ... Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engines intake manifold and Earths atmosphere. ... Revolutions per minute (abbreviated rpm, RPM, r/min, or min-1) is a unit of frequency, commonly used to measure rotational speed, in particular in the case of rotation around a fixed axis. ...

History

The ignition systems of older, non-computer controlled engines consists of a mechanical spark distributor which distributes spark to cylinders based on an initial timing advance, mechanical timing advance, and vacuum timing advance. In 1972, Chrysler introduced the electronic ignition system that controlled ignition timing and fuel delivery, replacing the mechanical spark distributor and therefore mechanical and vacuum timing advance [1]. This system led to the advanced automobile electronic systems of today’s automobiles. Ignition systems will continue to improve as ignition components become more technologically advanced. This article is about distributors in internal combustion engines. ... The Chrysler Corporation is a United States-based automobile manufacturer, since 1998 merged with Daimler_Benz into DaimlerChrysler. ...

Setting the Ignition Timing

Four Stroke Cycle

“Timing advance” refers to the number of degrees before top dead center (BTDC) that the spark will ignite the air-fuel mixture in the combustion chamber during the power stroke. “Timing retard” refers to the number of degrees after top dead center (ATDC) that the spark will ignite the air-fuel mixture during the power stroke. Timing advance is required because it takes time to burn the air-fuel mixture. Igniting the mixture before the piston reaches top dead center (TDC) will allow the mixture to become fully burnt soon after the piston reaches TDC. If the air-fuel mixture is ignited at the correct time, maximum pressure in the cylinder will occur sometime after the piston reaches TDC allowing the ignited mixture to push the piston down the cylinder. Ideally, the time at which the mixture should be fully burnt is about 20 degrees ATDC. This will utilize the engines power producing potential. If the ignition spark occurs at a position that is too advanced relative to piston position, the rapidly expanding air-fuel mixture can actually push against the piston causing detonation and lost power. If the spark occurs too retarded relative to the piston position, maximum cylinder pressure will occur after the piston is already traveling too far down the cylinder. This results in lost power, high emissions, and unburned fuel. The ignition timing will need to become increasingly advanced (relative to TDC) as the engine speed increases so that the air-fuel mixture has the correct amount of time to fully burn. Another reason for advancing the timing is because as the engine speed increases, fuel consumption increases. Since more fuel is present in the cylinder, the time required to fully burn the air-fuel mixture will be longer. The correct timing advance for a given engine speed will allow for maximum cylinder pressure to be achieved at the correct crankshaft angular position. In internal combustion engines, the air-fuel ratio refers to the proportion of air and fuel present during combustion. ... A power stroke is, in general, the stroke of a cyclic motor which generates force. ... It has been suggested that this article or section be merged into Engine knocking. ... Emission standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. ...

Mechanical Ignition Systems

Mechanical ignition systems use a mechanical spark distributor to distribute a high voltage current to the correct spark plug at the correct time. In order to set an initial timing advance or timing retard for an engine, the engine is allowed to idle and the distributor cap is adjusted to achieve the best ignition timing for the engine at idle speed. This process is called 'setting the base advance'. There are two methods of increasing timing advance past the base advance. The advances achieved by these methods are added to the base advance number in order to achieve a total timing advance number. The ignition system of an internal-combustion engine is an important part of the overall engine system that provides for the timely burning of the fuel mixture within the engine. ... This article is about distributors in internal combustion engines. ... This article or section should include material from Spark gap A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed aerosol gasoline by means of an electric spark. ... Distributor caps are used in automobile engine to cover the distributor and its internal rotor. ...

Mechanical Timing Advance

Distributor weights

An increasing mechanical advancement of the timing takes place with increasing engine speed. This is possible by using the law of inertia. Weights and springs inside the distributor cap rotate and affect the timing advance according to engine speed. The principle of inertia is one of the fundamental laws of classical physics which are used to describe the motion of matter and how it is affected by applied forces. ...

Vacuum Timing Advance

The second method used to advance the ignition timing is called vacuum timing advance. This method is sometimes (depending on the engine manufacturer) used in addition to mechanical timing advance. Vacuum advance works by using a vacuum source (typically the intake manifold) in the engine to advance the timing at mid engine load conditions. Vacuum advance is diminished at wide open throttle (WOT), causing the timing advance to return to the base advance in addition to the mechanical advance. In automotive engineering, an intake manifold or inlet manifold is a part of an engine that supplies the fuel/air mixture to the cylinders. ... Wide Open Throttle (WOT) refers to an internal combustion engines maximum intake of air and fuel that occurs when the throttle plates inside the carburetor or throttle body are wide open, providing the least resistance to the incoming air. ...

Electronic Ignition Systems

Timing Map

Newer engines typically use electronic ignition systems (ignition controlled by a computer). The computer has a timing map which is a chart with engine speed on one axis and engine load on another axis. Timing advance numbers are inserted in this chart. The computer will send a signal to the ignition coil at the indicated time in the timing map in order to spark the spark plug. Most computers from original equipment manufacturers (OEM) are not able to be modified so changing the timing advance is not possible. Aftermarket engine control units allow the user to make changes to the timing map. This allows the timing to be advanced or retarded based on various engine applications. The ignition system of an internal-combustion engine is an important part of the overall engine system that provides for the timely burning of the fuel mixture within the engine. ... An ignition coil (also called a spark coil) is an electrical device in a automobiles ignition system which transforms a storage batterys 12 volts to the thousands of volts needed to spark the spark plugs. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... An Engine Control Unit (ECU) also know as Engine Management System (EMS) is an electronic system which controls various aspects of an internal combustion engines operation. ...

Bibliography

Hartman, J. (2004). How to Tune and Modify Engine Management Systems. Motorbooks

External links

• Setting Ignition Timing Curves
• Ignition Timing